https://en.wikipedia.org/wiki/Barack_Obama
Tested 2026-09-20 11:34:16 using Chrome 152.0.7977.64 (script).(runtime settings)
Test mobile as a logged in userLogin the user with an empty browser cache, then visit Obama and Facebook
This page is slow to paint, janky to interact with, prone to layout shifts, loose on best practices, weak on user privacy and slow to respond from the server.
Visual metrics
Google Web Vitals
First contentful paint is poor (4.432 s). It is in the Google Web Vitals poor range, slower than 3 seconds.The page has a high time to first byte (TTFB) 2.509 s that you should look into to improve first contentful paint.
Largest contentful paint is poor 4.432 s. It is in the Google Web Vitals poor range, slower than 4 seconds.
The page has 14 CPU long tasks with the total of 2.044 s. The total blocking time is 1.291 s and 3 long tasks before first contentful paint with total time of 203 ms. However the CPU Long Task is depending on the computer/phones actual CPU speed, so you should measure this on the same type of the device that your user is using. Use Geckoprofiler for Firefox or Chromes tracelog to debug your long tasks.
Timings summary
| Metric | Min | Median | Mean | Max |
|---|---|---|---|---|
| First visual change | 4.433 s | 4.433 s | 4.433 s | 4.433 s |
| Last visual change | 12.000 s | 12.000 s | 12.000 s | 12.000 s |
| Speed index | 5.389 s | 5.389 s | 5.389 s | 5.389 s |
| Largest image | 4.433 s | 4.433 s | 4.433 s | 4.433 s |
| Heading | 7.333 s | 7.333 s | 7.333 s | 7.333 s |
| Largest contentful paint | 7.333 s | 7.333 s | 7.333 s | 7.333 s |
| Last meaningful paint | 7.333 s | 7.333 s | 7.333 s | 7.333 s |
| Visual readiness | 7.567 s | 7.567 s | 7.567 s | 7.567 s |
| Visual complete 85 | 7.367 s | 7.367 s | 7.367 s | 7.367 s |
| Visual complete 95 | 7.367 s | 7.367 s | 7.367 s | 7.367 s |
| Visual complete 99 | 7.367 s | 7.367 s | 7.367 s | 7.367 s |
Run 1 SpeedIndex median
The red band on the timeline marks when the main thread was busy with long tasks: moments when the page could not paint or respond, however the video looks.
Download videoUse --filmstrip.showAll to show all filmstrips.
Click a frame to seek the video to that moment. The dot marks frames where the page changed visually.
The whole recording in one image: every pixel is tinted by how often it changed. Amber changed once, deep red changed ten or more times. The scale is fixed, so heatmaps from different runs compare directly.
Flat amber is a page that painted once and stayed put. Red speckle in the shape of the text means the same pixels repainted over and over, usually invisible rendering noise that inflates Last Visual Change and Speed Index. A solid red block is a genuinely restless area, like an ad or a carousel.
How smoothly Chrome delivered frames to the screen during the test. Dropped counts only frames Chrome flags as affecting smoothness. On mostly-static pages the longest gap includes idle time where there was simply nothing to draw.
The server dominated the wait. The first byte took 2.509 s (57 % of the time to First Contentful Paint). Nothing can render before it arrives, and Google Web Vitals considers a TTFB over 800 ms in need of improvement. See the request timing on the Waterfall tab. First paint landed at 4.432 s; the 1 render-blocking request was done by 4.101 s and the remaining ~331 ms is style and layout work (167 ms of it measured style recalculation).
Style the browser had to recalculate before it could paint: many elements or a lot of time spent here points at expensive CSS on the critical rendering path. The recalculation count and the largest single one tell the two problems apart: one massive style change touching most of the page (few recalculations, the largest close to the total) needs different medicine than thousands of tiny ones (many recalculations, each tiny).
Style recalculation is not holding up your paint. 167 ms of restyling before the page painted, 3.8 % of the time to First Contentful Paint. Nothing here needs attention.
The recalculation work before first paint is 3.8 % of the time to First Contentful Paint.
Blocking requests delay both paints: the browser renders nothing until they arrive, so they push First Contentful Paint and everything after it, including the largest paint (LCP). Requests that block the parser inside the body stall everything after them in the document. Load JavaScript with defer or async, and keep non-critical CSS off the critical path with media attributes. Bars show when each request loaded on a clock that runs to the last paint; the gap after the bars is style and layout work.
| Request | When it loaded | Transfer | Download |
|---|---|---|---|
document | 4.725 s | 338.2 KB | 4.724 s |
1.178 s | 30.2 KB | 1.178 s | |
01.108 s2.216 sFCP · LCP 4.432 s |
How long Chrome spent testing each CSS selector against the page while recalculating styles. A selector with many match attempts and zero matches is evaluated against the document over and over for rules that never apply.
Not worth optimizing on this page. All selector matching cost 99 ms under the 7× CPU throttle, roughly 14 ms real time, and the worst single selector 24.59 ms. The tables are kept for reference.
| Selector | Time | Attempts | Matches |
|---|---|---|---|
.client-js.mf-expand-sections-clientpref-0 .mw-parser-output[data-mw-parsoid-version] > section > .mw-heading + div:not(.mf-collapsible-content):has(:target) | 24.59 ms | 272 | 0 |
.minerva-header .branding-box a > * | 2.20 ms | 1 518 | 2 |
.slider-button .cdx-button.cdx-button--icon-only span + span | 2.05 ms | 325 | 0 |
.content .center > * | 1.89 ms | 1 518 | 0 |
a:where(:not([role="button"]):not(.cdx-menu-item__content)) | 1.80 ms | 354 | 306 |
a:where(:not([role="button"]):not(.cdx-menu-item__content)):visited:hover | 1.67 ms | 708 | 0 |
.cdx-message__content | 1.65 ms | 9 | 9 |
.cdx-message__content > * | 1.63 ms | 1 518 | 9 |
.client-js.mf-expand-sections-clientpref-0 .mw-parser-output[data-mw-parsoid-version] > section > .mw-heading:has(:target) + div:not(.mf-collapsible-content) | 1.58 ms | 272 | 0 |
.last-modified-bar__text | 1.46 ms | 14 | 14 |
| Selector | Attempts | Time |
|---|---|---|
.skin-theme-clientpref-night .ns-100 .mw-parser-output :not(.notheme):not(a) | 1 518 | 0.09 ms |
blockquote > :only-child | 1 518 | 0.07 ms |
.content .center > * | 1 518 | 1.89 ms |
.client-js .outercollapse .innercollapse.mw-collapsible:not(.mw-made-collapsible) > :is(p, table, thead + tbody) | 1 518 | 0.08 ms |
blockquote > :first-child | 1 518 | 0.04 ms |
blockquote > :last-child | 1 518 | 0.05 ms |
.client-js .outercollapse .innercollapse.mw-collapsible:not(.mw-made-collapsible) :is(tr:not(:first-child), .mw-collapsible-content) | 1 518 | 0.04 ms |
body.mw-mmv-lightbox-open > :not(.mw-notification-area-overlay) | 866 | 0.05 ms |
.overlay-header h2 > * | 823 | 0.05 ms |
.overlay-issues .issue-details > ::first-line | 808 | 1.11 ms |
Why the browser had to recalculate style and layout: every DOM/style change invalidates some set of nodes, and the same class or attribute churning over and over is the pattern to hunt. Counts, not milliseconds: the time is in the style recalculation numbers above.
Chase what keeps changing after the page is up. 608 style recalculations and 1 057 layout invalidations fired after first paint, on a page the user was already looking at. The biggest driver is attribute title (431×). Start with the script under "Scripts causing invalidations" that keeps triggering it.
attribute: title431×attribute: style311×pseudo: has52×pseudo: disabled44×pseudo: enabled44×class: mf-collapsible-heading26×attribute: disabled21×class: mf-collapsible-content13×class: phase-pre-ready12×class: animated-111×class: state-no-source8×class: animated-24×attribute: controls4×pseudo: last-child2×pseudo: only-child2×Invalidations on a page the user was already looking at, the actionable half.
| Reason | Style recalculations | Layout |
|---|---|---|
| A :has() selector was re-evaluated:has() re-checks a whole subtree on any change inside it. Scope it tightly, or toggle a class in JavaScript instead. | 212 | – |
| A node was inserted into the page | 184 | – |
| Related style rule | 102 | – |
| An animation updated stylesAnimate transform and opacity so the compositor can run it off the main thread. | 40 | – |
| A stylesheet rule changed | 29 | – |
| An @keyframes rule changed | 19 | – |
| Attribute | 13 | – |
| JavaScript changed an inline styleSet a class instead of writing element.style, so the browser can batch the work. | 9 | – |
| An element entered layout | – | 938 |
| An element left layout | – | 58 |
| An SVG element changed | – | 19 |
| Unknown | – | 15 |
| An element's size changed | – | 16 |
| A style change forced layout | – | 10 |
| Slider value changed | – | 1 |
The page being constructed and styled for the first render. Expected work, shown for scale.
| Reason | Style recalculations | Layout |
|---|---|---|
| A node was inserted into the page | 4 | – |
| PlatformColorChange | 38 | – |
| A stylesheet rule changed | 1 | – |
| An element entered layout | – | 283 |
| Unknown | – | 2 |
jqueryinvalidations · all after first paintmobile.initinvalidations · all after first paintskins.minerva.scriptsinvalidations · all after first paintmobile.startupinvalidations · all after first paintext.personalDashboard.blueDotinvalidations · all after first paintext.readingLists.bookmarkinvalidations · all after first paintmediawiki.utilinvalidations · all after first paintext.relatedArticles.readMore.bootstrapinvalidations · all after first paintmediawiki.page.readyinvalidations · all after first paint4 animations run on the main thread instead of on the browser's fast path that animates without blocking other page work (the compositor); they can make the rendering you see above janky. See them on the CPU tab.
The coach helps you find performance problems on your web page using web performance best practice rules. And gives you advice on privacy and best practices. Tested using Coach-core version 9.2.1.
firstContentfulPaintFirst contentful paint is poor (4.432 s). It is in the Google Web Vitals poor range, slower than 3 seconds.The page has a high time to first byte (TTFB) 2.509 s that you should look into to improve first contentful paint.
The First Contentful Paint (FCP) metric measures the time from when the page starts loading to when any part of the page content is rendered on the screen. For this metric, "content" refers to text, images (including background images), <svg> elements, or non-white <canvas> elements.
largestContentfulPaintLargest contentful paint is poor 4.432 s. It is in the Google Web Vitals poor range, slower than 4 seconds.
Largest contentful paint is one of Google Web Vitals and reports the render time of the largest image or text block visible within the viewport, relative to when the page first started loading. To be fast according to Google, it needs to render before 2.5 seconds and results over 4 seconds is poor performance.
longTasksThe page has 14 CPU long tasks with the total of 2.044 s. The total blocking time is 1.291 s and 3 long tasks before first contentful paint with total time of 203 ms. However the CPU Long Task is depending on the computer/phones actual CPU speed, so you should measure this on the same type of the device that your user is using. Use Geckoprofiler for Firefox or Chromes tracelog to debug your long tasks.
Long CPU tasks locks the thread. To the user this is commonly visible as a "locked up" page where the browser is unable to respond to user input; this is a major source of bad user experience on the web today. However the CPU Long Task is depending on the computer/phones actual CPU speed, so you should measure this on the same type of the device that your user is using. To debug you should use the Chrome timeline log and drag/drop it into devtools or use Firefox Geckoprofiler.
modernImageFormatsThe page ships 44 images (out of 44) in JPEG/PNG/GIF without a modern alternative. Wrap them in a <picture> with a <source type="image/avif"> or "image/webp" before the legacy <img>, or serve modern formats from your image pipeline directly. AVIF and WebP usually deliver 25–50% smaller files at the same quality.
AVIF and WebP routinely deliver 25–50% smaller files than JPEG and PNG at the same perceived quality, and every browser version still under support understands at least one of them. Ship modern formats either through a <picture> element with <source type="image/avif"> / "image/webp" entries in front of the legacy <img>, or directly from a content-negotiating image pipeline that returns AVIF / WebP when the client accepts it. https://web.dev/articles/serve-images-webp
avoidScalingImagesThe page has 2 images that are scaled more than 100 pixels. It would be better if those images are sent so the browser don't need to scale them.
It's easy to scale images in the browser and make sure they look good in different devices, however that is bad for performance! Scaling images in the browser takes extra CPU time and will hurt performance on mobile. And the user will download extra kilobytes (sometimes megabytes) of data that could be avoided. Don't do that, make sure you create multiple version of the same image server-side and serve the appropriate one.
cacheHeadersThe page has 2 requests that are missing a cache time. Configure a cache time so the browser doesn't need to download them every time. It will save 55.4 kB the next access.
The easiest way to make your page fast is to avoid doing requests to the server. Setting a cache header on your server response will tell the browser that it doesn't need to download the asset again during the configured cache time! Always try to set a cache time if the content doesn't change for every request.
cacheHeadersLongThe page has 15 requests that have a shorter cache time than one year (but still a cache time).
Setting a cache header is good. Setting a long cache header (a year) is even better because the asset will stay in the browser cache across visits. For content-hashed URLs (e.g. app.4af2.css) you can safely use Cache-Control: max-age=31536000, immutable. For unversioned URLs that may change, use a revalidating strategy instead.
decodingAsyncThe page has 5 images (out of 48) without a decoding hint. Add decoding="async" to non-critical images so the browser can decode them off the main thread.
Setting decoding="async" on an <img> tells the browser it can decode the image off the main thread, which keeps the page responsive to user interactions while images are being processed. The default ("auto") leaves the choice to the browser. https://developer.mozilla.org/en-US/docs/Web/HTML/Element/img#decoding
optimalCssSizehttps://en.wikipedia.org/w/load.php?lang=en&modules=ext.cite.parsoid.styles%7Cext.cite.styles%7Cext.echo.styles.alert%2Cbadge%7Cext.personalDashboard.menuIcon%7Cext.phonos.icons%2Cstyles%7Cext.readingLists.bookmark.icons%2Cstyles%7Cext.relatedArticles.styles%7Cext.tmh.player.styles%7Cext.wikimediaBadges%7Cext.wikimediaBadges.ulsV2%7Cext.wikimediamessages.styles%7Cmediawiki.codex.messagebox.styles%7Cmediawiki.hlist%7Cmediawiki.skinning.content.parsoid%7Cmediawiki.skins.legacy%7Cmobile.init.styles%7Coojs-ui.styles.icons-alerts%7Cskins.minerva.codex.styles%7Cskins.minerva.content.styles.images%7Cskins.minerva.icons%2Cstyles%7Cskins.minerva.loggedin.styles%7Cwikibase.client.init&only=styles&skin=minerva size is 31 kB (30974) and that is bigger than the limit of 25 kB. Try to keep each CSS response under 25 kB.
Render-blocking CSS holds up the first paint until it has fully downloaded, parsed and applied, so smaller CSS files mean a faster start. Split your CSS into a small critical bundle inlined or eagerly loaded, with the rest lazy-loaded.
| URL | Transfer | Content |
|---|---|---|
| https://en.wikipedia.org/w/load.php...ia.org/w/load.php | 30.2 KB | 248.6 KB |
privateAssetsThe page has 2 requests with private headers. The main page has a private header. It could be right in some cases where the user can be logged in and served specific content. But if your asset is static it should never be private. Make sure that the assets really should be private and only used by one user. Otherwise, make it cacheable for everyone.
If you set private headers on content, that means that the content are specific for that user. Static content should be able to be cached and used by everyone. Avoid setting the cache header to private.
inlineCssThe page has both inline CSS and CSS requests even though it uses a HTTP/2-ish connection. If you have many users on slow connections, it can be better to only inline the CSS. Run your own tests and check the waterfall graph to see what happens.
In the early days of the Internet, inlining CSS was one of the ugliest things you can do. That has changed if you want your page to start rendering fast for your user. Always inline the critical CSS when you use HTTP/1 and HTTP/2 (avoid doing CSS requests that block rendering) and lazy load and cache the rest of the CSS. It is a little more complicated when using HTTP/2. Does your server support HTTP push? Then maybe that can help. Do you have a lot of users on a slow connection and are serving large chunks of HTML? Then it could be better to use the inline technique, becasue some servers always prioritize HTML content over CSS so the user needs to download the HTML first, before the CSS is downloaded.
lazyLoadingImagesThe page has 1 below-the-fold image without loading="lazy". Add loading="lazy" so the browser defers downloading and decoding them until the user scrolls them into view.
Adding loading="lazy" to an <img> tells the browser not to download or decode it until it is close to the viewport. For images that the user may never see (deep in the page, behind a tab, in a footer carousel), this saves bandwidth and main-thread time during initial render. The LCP image and any image in the initial viewport should NOT be lazy-loaded — that delays the first paint. https://developer.mozilla.org/en-US/docs/Web/HTML/Element/img#loading
metaDescriptionThe page is missing a meta description.
Use a page description to make the page more relevant to search engines.
cumulativeLayoutShiftYou have a cumulative layout shift score (0.1896) that needs improvements. It is in the Google Web Vitals needs improvement range, shift higher than 0.1. You should manually check the filmstrip or video and check if it will affect the user.
Cumulative Layout Shift measures the sum total of all individual layout shift scores for unexpected layout shift that occur. The metric is measuring visual stability by quantify how often users experience unexpected layout shifts. It is one of Google Web Vitals.
unnecessaryHeadersThere are 16 responses that sets both a max-age and expires header. There are 20 responses that sets a server header.
Do not send headers that you don't need. We look for p3p, cache-control and max-age, pragma, server and x-frame-options headers. Have a look at Andrew Betts - Headers for Hackers talk as a guide https://www.youtube.com/watch?v=k92ZbrY815c or read https://www.fastly.com/blog/headers-we-dont-want.
imageAltTextThe page has 2 images without an alt attribute. Add alt="..." with a description, or alt="" if the image is purely decorative.
Every <img> needs an alt attribute. Use alt="meaningful description" for content images so assistive technologies can announce them, or alt="" (or role="presentation" / aria-hidden="true") for purely decorative images so they are skipped. A missing alt attribute leaves screen reader users with no information at all. https://developer.mozilla.org/en-US/docs/Web/HTML/Element/img#alt
longHeadershttps://en.wikipedia...wiki/Barack_Obama has a header content-security-policy that is 4206 characters long.
Do not send response headers that are too long.
crossOriginEmbedderPolicyHeaderSet a Cross-Origin-Embedder-Policy header (typically require-corp or credentialless) on the document response to control cross-origin embedding.
Cross-Origin-Embedder-Policy (COEP) makes the page refuse to load cross-origin subresources unless they explicitly opt in via CORP or CORS. Together with Cross-Origin-Opener-Policy it puts the page in a cross-origin isolated context, which mitigates cross-window side-channel attacks (Spectre) and unlocks high-resolution timers and SharedArrayBuffer. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cross-Origin-Embedder-Policy
crossOriginOpenerPolicyHeaderSet a Cross-Origin-Opener-Policy header (typically same-origin) on the document response to isolate the page from cross-origin windows.
Cross-Origin-Opener-Policy (COOP) lets a page sever its window-group ties to cross-origin documents that opened it or that it opens. Together with Cross-Origin-Embedder-Policy it puts the page in a cross-origin isolated context, which mitigates cross-window side-channel attacks (Spectre) and unlocks high-resolution timers and SharedArrayBuffer. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cross-Origin-Opener-Policy
crossOriginResourcePolicyHeaderSet a Cross-Origin-Resource-Policy header (same-origin, same-site or cross-origin) on the document response to limit who may embed it.
Cross-Origin-Resource-Policy (CORP) is a per-response opt-in that tells the browser which origins are allowed to embed the resource. It blocks cross-origin or cross-site no-cors embedding (img, script, iframe, etc.) and is one of the building blocks of cross-origin isolation. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cross-Origin-Resource-Policy
permissionsPolicyHeaderSet a Permissions-Policy header to control which browser features the page can use.
The Permissions-Policy response header (the successor to Feature-Policy) lets a site explicitly opt in or out of powerful browser features such as camera, microphone, geolocation, payment and clipboard. Setting a strict policy reduces the attack surface and limits what embedded third parties can do. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Permissions-Policy
referrerPolicyHeaderSet a referrer-policy header to make sure you do not leak user information.
Referrer Policy is a new header that allows a site to control how much information the browser includes with navigations away from a document and should be set by all sites. https://scotthelme.co.uk/a-new-security-header-referrer-policy/.
contentSecurityPolicyHeaderThe policy allows 'unsafe-inline', which lets the browser execute inline scripts and styles directly from the page. Move to nonces or hashes plus 'strict-dynamic' so that inline injection cannot run. The policy allows 'unsafe-eval', which lets the page call eval() and Function(). Almost no application needs this; remove it.
A Content-Security-Policy response header tells the browser which sources of script, style, and other content are allowed. The most effective form is a strict CSP using nonces or hashes together with strict-dynamic; the worst is a missing header, with unsafe-inline and unsafe-eval close behind. https://web.dev/articles/strict-csp
A snapshot of what the browser actually built for this page: the document, how big and deep the DOM tree is and what it kept in storage. Big, deep trees are slower to style and lay out, so the counts Chrome warns about carry a flag.
Document
What the page says it is and how large it rendered.
DOM structure
How much markup the browser has to build, style and lay out.
What the page stored on the client, and the network it was tested on.
Data collected using
Coach-core version 9.2.1. With updated code from
Webappanalyzer 2026-05-04. Use
--browsertime.firefox.includeResponseBodies html or
--browsertime.chrome.includeResponseBodies html to help Wappalyzer find more information about technologies used.
Data from run 1
0.0s4.5s5.1s5.7s6.1s7.2s7.8s12.0sWhen the page main content is rendered, collected via the Largest Contentful Paint API. Read more about Largest Contentful Paint.
body > div#mw-mf-viewport > div#mw-mf-page-center > main#content > div:eq(0) > div#siteNotice > div:eq(1) > div
The LCP element is highlighted in the screenshot. If nothing is highlighted the element was removed before the screenshot or the LCP API couldn't find it.
How much the page's content shifts as it loads, collected via the Cumulative Layout Shift API.
One shift is 100% of your 0.190 CLS. div:eq(1) moved at 7.284 s. Reserve space for whatever renders into that spot, a fixed height or an aspect-ratio box, so later content stops pushing the page around.
Worst first, showing shifts of 0.01 and up. Each percentage is that shift's exact share of the score.
body > div#mw-mf-viewport > div#mw-mf-page-center > main#content > div:eq(0) > div#siteNotice > div:eq(1)body > div#mw-mf-viewport > div#mw-mf-page-center > main#content > div:eq(1)body > div#mw-mf-viewport > div#mw-mf-page-center > main#content > div#bodyContentbody > div#mw-mf-viewport > div#mw-mf-page-center > main#content > div:eq(1) > nav > ul#p-viewsbody > div#mw-mf-viewport > div#mw-mf-page-center > main#content > div:eq(0) > div#siteNotice > div:eq(1) > span
Elements that shifted by more than 0.01 are highlighted in the screenshot. If an element shifted outside the viewport, it won't appear here. Check the video or filmstrip to see the shift.
Timing data the server chose to expose through Server-Timing response headers on the main document — typically backend time, cache status or experiment flags.
| Name | Duration | Description |
|---|---|---|
cache | 0 ms | pass |
host | 0 ms | cp3070 |
co_id | 0 ms | 1304882960 |
There are no custom configured scripts.
There are no custom extra metrics from scripting.
How the page is built.
https://en.wikipedia.org/wiki/Barack_Obama
| Header | Value |
|---|---|
accept-ch | |
accept-ranges | bytes |
age | 6 |
cache-control | private, s-maxage=0, max-age=0, must-revalidate, no-transform |
content-encoding | gzip |
content-language | en |
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date | Sun, 20 Sep 2026 11:34:18 GMT |
expires | Thu, 01 Jan 1970 00:00:00 GMT |
last-modified | Sun, 20 Sep 2026 11:33:32 GMT |
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| type | min | median | max |
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JavaScript and CSS coverage from the extra profile run made by --enableProfileRun, not from the timed iterations. For JS, Chrome tracks which blocks of each script actually ran: a byte is unused when the innermost block of code around it never ran. For CSS, Chrome records every selector that no element on the page matched during the iteration. Enable with --chrome.coverage on every run, or --enableProfileRun to keep the main run's timing metrics untouched. Unused bytes still cost network, parse and compile time for no benefit. Expand the section below for the full picture.
sitespeed.io drives Chrome's V8 profiler and CSS rule tracker via the DevTools Protocol, the same machinery the DevTools Coverage panel uses. The two columns are populated by two different mechanisms.
Browsertime calls Profiler.startPreciseCoverage with detailed (block-level) mode at the start of the iteration and Profiler.takePreciseCoverage at the end. V8 returns nested ranges per function: an outer range covering the function body and inner ranges for sub-blocks (if/else, switch arms, ternaries). Each range has an execution count. A byte is "used" if the innermost range that covers it has count > 0, "unused" if it has count = 0, so we catch both functions that never ran AND dead branches inside functions that did.
Browsertime calls CSS.startRuleUsageTracking at the start of the iteration and CSS.stopRuleUsageTracking at the end. Chrome returns a flat list of rule-text ranges with a used flag: a rule is "used" if at least one element on the page matched it during the iteration. Both inline <style> blocks and external stylesheets are included.
Coverage reflects only what executed during this run. Code behind a button click stays unused unless the iteration clicked the button. The collection window opens before navigation and closes when measure.stop() is reached, so the only way to count interactions is to drive them between measure.start() and measure.stop() inside a navigation script (pass a .js file as the input instead of a plain URL). Clicks, form fills and waits placed there all count toward "used". --preScript runs before the URL is loaded so it can't interact with the page being measured, and --postScript runs after coverage has already been collected, so neither helps here. Detailed coverage also tells V8 to skip some optimisations, which drifts timing metrics like LCP and TBT; that's why --enableProfileRun is the safer option for production measurement (it collects coverage in a separate iteration that doesn't count towards the medians).
2.3 MB of script and style shipped, and 1.1 MB of it never ran on this page. The biggest win is load.php[styles:ext.cite.parsoid.styles]: 248.6 KB delivered, 200.3 KB unused.
| URL | Total | Used | Unused | Unused % | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| load.php[scripts:oojs-ui-core] | 186.8 KB | 35.8 KB | 151.0 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:ext.cite.ux-enhancements] | 169.3 KB | 80.4 KB | 89.0 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
11 modules in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:moment] | 97.5 KB | 24.4 KB | 73.1 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:oojs-ui-widgets] | 92.4 KB | 36.5 KB | 55.8 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:ext.echo.ui] | 65.1 KB | 25.1 KB | 40.1 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:ext.wikimediaEvents] | 58.1 KB | 20.5 KB | 37.6 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:mediawiki.api] | 27.4 KB | 5.1 KB | 22.2 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:ext.uls.interface] | 47.7 KB | 25.7 KB | 21.9 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:mobile.startup] | 60.5 KB | 39.8 KB | 20.7 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:ext.visualEditor.targetLoader] | 23.3 KB | 2.7 KB | 20.5 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:skins.minerva.scripts] | 57.0 KB | 40.7 KB | 16.3 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:ext.echo.dm] | 25.1 KB | 9.2 KB | 15.9 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:ext.testKitchen] | 32.7 KB | 19.4 KB | 13.4 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:ext.growthExperiments.SuggestedEditSession] | 16.1 KB | 4.0 KB | 12.1 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:ext.centralNotice.display] | 30.8 KB | 19.0 KB | 11.8 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:mobile.init] | 19.0 KB | 7.5 KB | 11.5 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:oojs] | 15.2 KB | 3.9 KB | 11.3 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:mediawiki.template.mustache] | 12.4 KB | 1.9 KB | 10.5 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:mediawiki.util] | 16.7 KB | 6.7 KB | 10.1 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:mediawiki.page.ready] | 17.1 KB | 7.3 KB | 9.8 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:ext.navigationTiming] | 11.0 KB | 1.7 KB | 9.3 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:ext.echo.api] | 12.2 KB | 3.0 KB | 9.2 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:mediawiki.DateFormatter] | 13.5 KB | 4.5 KB | 9.0 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:mediawiki.jqueryMsg] | 30.1 KB | 22.3 KB | 7.8 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| load.php[scripts:mmv.bootstrap] | 28.7 KB | 21.7 KB | 7.0 KB | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 module in this bundle, by unused bytes
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| URL | Total | Used | Unused | Unused % |
|---|---|---|---|---|
| load.php[styles:ext.cite.parsoid.styles] | 248.6 KB | 48.3 KB | 200.3 KB | |
| (inline stylesheet) 4 stylesheets | 130.1 KB | 11.9 KB | 118.2 KB | |
| load.php[styles:site.styles] | 6.6 KB | 955 B | 5.7 KB | |
| TemplateStyles:r1358620234 | 1.3 KB | 135 B | 1.2 KB | |
| TemplateStyles:r1034237262 | 637 B | 103 B | 534 B | |
| TemplateStyles:r1314755338 | 851 B | 363 B | 488 B | |
| TemplateStyles:r1290232777 | 783 B | 378 B | 405 B | |
| TemplateStyles:r1368532237 | 303 B | 114 B | 189 B | |
| TemplateStyles:r1298804929 | 210 B | 58 B | 152 B | |
| TemplateStyles:r1126788409 | 205 B | 205 B | 0 b |
A high unused-% on one run means this iteration loaded code that didn't get exercised, typical on first-load journeys before any user interaction. Drive the real flow by passing a navigation script as the input instead of a plain URL, with clicks and form fills placed between measure.start() and measure.stop(); anything in that window counts toward "used". The advice below is for code that's still unused after a representative run.
import(). Bundlers turn the import boundary into a separate chunk.defer or async so the parser doesn't block on code the page doesn't need yet.media= tricks or rel="preload" swaps.Tasks ≥ 50 ms blocking the main thread, collected via the Long Task API.
A long animation frame (LOAF) is a frame that took ≥ 50 ms from input to the next paint. The part beyond the threshold is blocking time, the number that hurts Interaction to Next Paint and Total Blocking Time. Break long tasks up (scheduler.yield(), smaller chunks) or move the work off the main thread. Read more about the Long Animation Frames API.
| Script | Frames | Time running | Blocking (share by run time) | Forced style & layout | Triggered by |
|---|---|---|---|---|---|
| load.php[startup] | 6 | 925.7 ms | 644.7 ms | 51 ms | script tag, timer or animation callback |
| load.php[scripts:ext.cite.ux-enhancements] | 4 | 680.2 ms | 481.3 ms | 33.6 ms | timer or animation callback, script tag |
| load.php[scripts:ext.testKitchen] | 1 | 5.3 ms | 4.4 ms | – | timer or animation callback |
| inline script in the document | 1 | 10.8 ms | 1.9 ms | – | script tag |
A frame's blocking time is split between its scripts by their share of the frame's work, capped at each script's own run time — blocking from work no script owns (HTML parsing, browser internals) stays unattributed. The per-script blocking view below uses the same attribution.
The browser did not report which script was responsible for this frame — typically its own style/layout work, or a cross-origin script it will not name.
The browser did not report which script was responsible for this frame — typically its own style/layout work, or a cross-origin script it will not name.
How much each script blocked the main thread, derived from the Long Animation Frame API. Each frame's blocking time is split between its scripts by their share of the frame's work, capped at each script's own run time — blocking from work no script owns (HTML parsing, browser internals) is not attributed (older data credits the script that started the frame). The closest answer to "which script should I fix to improve TBT" the platform exposes.
Total Blocking Time attributed per script from the Chrome trace: every main-thread task longer than 50 ms blocks input for the remainder, and each blocking task is credited to the script whose own code ran the longest during that task.
All main-thread work during the full page load, not just the share that blocked input. Calculated from the Chrome trace.
parseHTMLstyleLayoutscriptParseCompilescriptEvaluationpaintCompositeRendergarbageCollectionotherMain-thread CPU time attributed to the individual modules inside concatenated JavaScript bundles (MediaWiki ResourceLoader), so a heavy bundle can be traced to the modules that actually cost the time.
The data comes from the extra profile run, not from the timed iterations.
| Module | Version | Self time |
|---|---|---|
jquery | 16rou | 703.7 ms |
| – | 229.6 ms |
| Module | Version | Self time |
|---|---|---|
mediawiki.storage | dnxpi | 7.8 ms |
| – | 0.1 ms |
| Module | Version | Self time |
|---|---|---|
ext.wikimediaEvents | 1yvhb | 5.9 ms |
| Module | Version | Self time |
|---|---|---|
ext.centralNotice.startUp | trejq | 5.2 ms |
| Module | Version | Self time |
|---|---|---|
ext.navigationTiming | 18ja5 | 2.5 ms |
| – | 0.1 ms |
| Module | Version | Self time |
|---|---|---|
skins.minerva.scripts | n2w9g | 1.6 ms |
| Module | Version | Self time |
|---|---|---|
ext.eventLogging | 1xqug | 1.3 ms |
| Module | Version | Self time |
|---|---|---|
ext.testKitchen | m6xrf | 0.5 ms |
The functions where main-thread JavaScript time was actually spent, sampled by Chrome's JavaScript profiler. Self time is spent in the function itself; total time includes the functions it called. For loader/dispatcher functions whose total dwarfs their self time, the runs line shows the top functions and modules (up to five, ≥ 1 ms) the total was actually spent running.
| Function | Where | Self time | Total time |
|---|---|---|---|
indirectEvalruns: load.php[scripts:oojs-ui-core.styles] (2.6 ms), load.php[scripts:mediawiki.base] (2.5 ms), load.php[scripts:ext.echo.mobile] (2.1 ms), load.php[scripts:ext.eventLogging.metricsPlatform] (1.7 ms), load.php[scripts:oojs-ui.styles.icons-moderation] (1.7 ms) | load.php[startup] | 145.3 ms | 186.6 ms |
querySelectorAll | 121.9 ms | 121.9 ms | |
setAttribute | 107.3 ms | 107.3 ms | |
setItem | 102.6 ms | 102.6 ms | |
insertBefore | 94.6 ms | 94.6 ms | |
runScriptruns: load.php[scripts:mobile.init] (178.4 ms), load.php[scripts:ext.cite.ux-enhancements] (58.5 ms), load.php[scripts:skins.minerva.scripts] (28.0 ms), load.php[scripts:ext.wikimediaEvents.emailConfirmationBanner] (26.5 ms), load.php[scripts:ext.wikimediaEvents] (26.5 ms) | load.php[startup] | 85.1 ms | 621.5 ms |
flushWritesruns: setItem (101.8 ms), load.php[startup] (4.1 ms) | load.php[startup] | 60.6 ms | 166.5 ms |
findruns: querySelectorAll (111.5 ms), load.php[scripts:ext.cite.ux-enhancements] (13.6 ms), getElementsByTagName (6.6 ms) | load.php[scripts:ext.cite.ux-enhancements] | 59.2 ms | 191.0 ms |
(anonymous) | load.php[scripts:mobile.startup] | 54.2 ms | 54.2 ms |
doPropagationruns: load.php[startup] (326.9 ms), load.php[scripts:mediawiki.base] (2.1 ms) | load.php[startup] | 41.3 ms | 370.3 ms |
replaceChild | 39.9 ms | 39.9 ms | |
setTimeout | 37.4 ms | 37.4 ms | |
requireruns: load.php[scripts:ext.wikimediaEvents] (9.7 ms), load.php[scripts:ext.eventLogging] (3.5 ms), load.php[scripts:ext.centralNotice.display] (2.1 ms), load.php[scripts:ext.eventLogging.metricsPlatform] (1.8 ms) | load.php[startup] | 32.9 ms | 60.8 ms |
implruns: load.php[startup] (4.0 ms), load.php[scripts:ext.echo.mobile] (1.7 ms), load.php[scripts:mobile.startup] (1.6 ms), load.php[scripts:ext.uls.interface] (1.5 ms), load.php[scripts:ext.readingLists.bookmark] (1.4 ms) | load.php[startup] | 32.7 ms | 44.6 ms |
load | load.php[startup] | 32.3 ms | 32.3 ms |
How much setTimeout/setInterval work the page runs, credited to the script that scheduled each timer. Many zero-delay timers mean work sliced into a machine-gun of tiny tasks; repeating timers are polling.
| Set by | Delay | Type | Times set | Times fired | Fire time |
|---|---|---|---|---|---|
jquery | 0 ms | once | 58 | 58 | 935.5 ms |
SafeStorage in mediawiki.storage | 2000 ms | once | 2 | 2 | 4.0 ms |
eval in ext.navigationTiming | 0 ms | once | 1 | 1 | 2.5 ms |
requestUpdate in load.php[startup]:22 | 2000 ms | once | 2 | 2 | 0.1 ms |
run in ext.wikimediaEvents | 60000 ms | once | 1 | 0 | 0.0 ms |
setActive in ext.wikimediaEvents | 100000 ms | once | 1 | 0 | 0.0 ms |
A forced reflow happens when JavaScript reads a layout-triggering property (offsetTop, getBoundingClientRect, …) inside a handler, forcing the browser to synchronously recompute layout. The scripts below caused most of the page's reflows. Fix them in priority order.
Each long animation frame reports how much time each script spent forcing synchronous style and layout, i.e. JavaScript reading layout-triggering properties mid-execution. Same actionable answer as forced reflows above but measured directly by the browser instead of inferred from the trace.
Main-thread CPU time from the Chrome trace split by domain. First party is wikipedia.org.
Animations that fell back from the compositor to the main thread, blocking each frame instead of running on the GPU.
Each chip below is a CSS property the page tried to animate that Chrome couldn't hand to the compositor. Swap it for a transform or opacity equivalent where you can.
color2×Want to dig deeper? Download the Chrome trace and drag-and-drop it into Performance in DevTools.